DoctorMuffn
06-28-2007, 04:57 PM
I know I'm new and most of you could care less that I'm posting something. Not to mention my loyalties to this forum have yet to be decided by it's members. And really I just want to sell my damned wheels.
However, I cut my teeth in the classroom, during apprenticeships, and on message forums. My devotion is to acquiring knowledge. And once acquired it is my pleasure to share it. So here's a tip; do with it what you will.
I'm posting this because I'm tired of seeing, "I pulled a MAF code so I replaced it but my car still runs like shit," types of responses. So let's get some basics about diagnostics straight from the beginning. Most of us know that all 4-stroke, spark ignition, internal combustion engines require three main things to function properly:
1. Air
2. Fuel
3. Spark
This is always your starting point from any diagnostic standpoint. And when you get frustrated and tunnel vision takes hold I advise you step back, take a break from your car and then come back to these three requirements for your engine to run properly.
From Clean Air Car Course Training Manual chapter 11 "Basics of Diagnosis" page 262
PERFORM BASIC INSPECTION
1. Verify Customer Complaint
2. Perform Visual Inspection (MOST IMPORTANT STEP and most overlooked because of it's simplicity... Afterall, I've got a Lamborghini so the problem must be complex and invisible since it runs on the atomic energy derived from splitting uranium in my flux capacitor).
3. Test Engine Sub-Systems:
a. Mechanical Condition (compression get a gauge or use your finger) !AIR!
b. Ignition Output (put the sparkplug on your tongue) !SPARK!
c. Fuel Delivery (remove injector from fuel rail and place in ear) !FUEL!
4. Check Air Induction System for Leaks !AIR!
5. Check and Adjust Basic Engine Settings:
a. Ignition Timing !SPARK!
b. Idle Speed !ALL 3 WORKING IN CONJUNCTION!
CHECK FOR TROUBLE CODES
1. If equipped with self-diagnostics, check for trouble codes. (The work is partly done for you as long as you first did a visual... do not skip the visual)
2. Repair cause of trouble code(s). (Not always the component most often a problem with the wiring, harness, or some other part of the circuit governing the component related to that code; especially if someone has been in there tinkering with stuff. But how do I know what part? Start with a visual to see what looks out of place).
3. Clear control unit memory. (Do this and give the repair a chance to prove itself by driving around. If the light comes back on or you hook up the reader and a code is pending it's probably not fixed so repeat the steps by first checking the code).
And the most important thing is knowledge... The right knowledge. If you like working on your car get a haynes manual. If you really like working on your car get the factory service manual and stop wasting your time with rabbit trails and incorrect information. But that's not enough. Check it out before it breaks. See what normal and properly functioning look and feel like. Then break something or better yet merely disconnect something and see what happens. Engine light? Code? Driveability concern?
Don't know how an engine works? Try
http://www.howstuffworks.com/ and search Engine
What's OBD? Try
http://en.wikipedia.org/wiki/On_Board_Diagnostics
http://www.obd-codes.com/
That's a Great Start!
However, I cut my teeth in the classroom, during apprenticeships, and on message forums. My devotion is to acquiring knowledge. And once acquired it is my pleasure to share it. So here's a tip; do with it what you will.
I'm posting this because I'm tired of seeing, "I pulled a MAF code so I replaced it but my car still runs like shit," types of responses. So let's get some basics about diagnostics straight from the beginning. Most of us know that all 4-stroke, spark ignition, internal combustion engines require three main things to function properly:
1. Air
2. Fuel
3. Spark
This is always your starting point from any diagnostic standpoint. And when you get frustrated and tunnel vision takes hold I advise you step back, take a break from your car and then come back to these three requirements for your engine to run properly.
From Clean Air Car Course Training Manual chapter 11 "Basics of Diagnosis" page 262
PERFORM BASIC INSPECTION
1. Verify Customer Complaint
2. Perform Visual Inspection (MOST IMPORTANT STEP and most overlooked because of it's simplicity... Afterall, I've got a Lamborghini so the problem must be complex and invisible since it runs on the atomic energy derived from splitting uranium in my flux capacitor).
3. Test Engine Sub-Systems:
a. Mechanical Condition (compression get a gauge or use your finger) !AIR!
b. Ignition Output (put the sparkplug on your tongue) !SPARK!
c. Fuel Delivery (remove injector from fuel rail and place in ear) !FUEL!
4. Check Air Induction System for Leaks !AIR!
5. Check and Adjust Basic Engine Settings:
a. Ignition Timing !SPARK!
b. Idle Speed !ALL 3 WORKING IN CONJUNCTION!
CHECK FOR TROUBLE CODES
1. If equipped with self-diagnostics, check for trouble codes. (The work is partly done for you as long as you first did a visual... do not skip the visual)
2. Repair cause of trouble code(s). (Not always the component most often a problem with the wiring, harness, or some other part of the circuit governing the component related to that code; especially if someone has been in there tinkering with stuff. But how do I know what part? Start with a visual to see what looks out of place).
3. Clear control unit memory. (Do this and give the repair a chance to prove itself by driving around. If the light comes back on or you hook up the reader and a code is pending it's probably not fixed so repeat the steps by first checking the code).
And the most important thing is knowledge... The right knowledge. If you like working on your car get a haynes manual. If you really like working on your car get the factory service manual and stop wasting your time with rabbit trails and incorrect information. But that's not enough. Check it out before it breaks. See what normal and properly functioning look and feel like. Then break something or better yet merely disconnect something and see what happens. Engine light? Code? Driveability concern?
Don't know how an engine works? Try
http://www.howstuffworks.com/ and search Engine
What's OBD? Try
http://en.wikipedia.org/wiki/On_Board_Diagnostics
http://www.obd-codes.com/
That's a Great Start!